There is known technology for directly forming copper plating on the surface of aluminum. For example, one method is described in Japanese Unexamined Patent Application Publication H2-240290 for directly copper-plating aluminum through pretreatment by alkali degreasing, washing with a surfactant, acid washing or water washing, followed by using a copper pyrophosphate plating bath containing 10-500 g/L phosphoric acid and/or a phosphate to perform plating at a current density of 0.1-2.0 A/dm2, and then heat-treating the aluminum. Embodiment 1 of this publication describes the formation of a copper plating layer approximately 10 μm thick on an aluminum plate. This method allows for the formation of a uniform copper plating layer with very good adhesion between the aluminum substrate and copper plating, as well as an appealing appearance.